Simple SummaryThe immense rainforest ecosystems of tropical America represent some of the greatest concentrations of biodiversity on the planet. Prominent among these are evolutionary radiations of freshwater fishes, including electric eels, piranhas, stingrays, and a myriad of small-bodied and colorful tetras, cichlids, and armored catfishes. In all, the many thousands of these forms account for nearly 10% of all the vertebrate species on Earth. This article explores the complimentary roles that ecological and geographic filters play in limiting dispersal in aquatic species, and how these factors contribute to the accumulation of species richness over broad geographic and evolutionary time scales.AbstractThe Neotropical freshwater ichthyofauna has among the highest species richness and density of any vertebrate fauna on Earth, with more than 5,600 species compressed into less than 12% of the world's land surface area, and less than 0.002% of the world's total liquid water supply. How have so many species come to co-exist in such a small amount of total habitat space? Here we report results of an aquatic faunal survey of the Fitzcarrald region in southeastern Peru, an area of low-elevation upland (200–500 m above sea level) rainforest in the Western Amazon, that straddles the headwaters of four large Amazonian tributaries; the Juruá (Yurúa), Ucayali, Purús, and Madre de Dios rivers. All measures of fish species diversity in this region are high; there is high alpha diversity with many species coexisting in the same locality, high beta diversity with high turnover between habitats, and high gamma diversity with high turnover between adjacent tributary basins. Current data show little species endemism, and no known examples of sympatric sister species, within the Fitzcarrald region, suggesting a lack of localized or recent adaptive divergences. These results support the hypothesis that the fish species of the Fitzcarrald region are relatively ancient, predating the Late Miocene-Pliocene (c. 4 Ma) uplift that isolated its several headwater basins. The results also suggest that habitat specialization (phylogenetic niche conservatism) and geographic isolation (dispersal limitation) have contributed to the maintenance of high species richness in this region of the Amazon Basin.
Herein Gymnotus chaviro is described from the Alto Yuruá (upper rio Juruá) of southeastern Peru, where it is locally abundant in terra firme streams and floodplain oxbow lakes, and occurs sympatrically and syntopically with the type species of the genus G. carapo. The new species is diagnosed by a unique combination of morphometric, meristic, and osteological traits, and a characteristic color pattern in which the dark band-pairs are unbranched and incompletely separated, and the pale inter-bands rarely reach to the dorsal mid-line on the anterior half of the body, being crescent-shaped in abdominal area. Gymnotus chaviro is a member of the G. carapo species group, with which it shares the presence of two pores in the dorsolateral portion of the preopercle, dark pigment bands with wavy margins that become broken and/or loose contrast with the ground color through growth, a clear patch at the caudal end of an otherwise darkly pigmented anal fin, and more than four arrowhead-shaped (anteroposteriorly compressed) teeth in the anterior portion of the dentary. Gymnotus chaviro is most similar in external appearance to G. curupira of lowland Western Amazonia in possessing a slender lateral profile (mean body depth less than 9% total length), a similar color pattern (median number of bands 19 with bands less distinct on dorsum), a large inter-orbital distance (mean greater than 41% head length), a broad head (mean head width greater than 65% head length) and a large mouth (mean mouth width greater than 43% head length). This new species can also be distinguished from G. curupira by the configuration of the preopercular pores, and by several meristic traits of squamation and fin rays. This is the first gymnotiform species described from the interior of the Fitzcarrald Arch, and the only gymnotiform species known to date that is endemic to this upland region of the western Amazon.En el presente trabajo se describe Gymnotus chaviro de Alto Yuruá (parte alta del Río Juruá) en el sureste de Peru. Esta especie es abundante en arroyos de tierra firme y llanuras con lagos en herradura, ocurre de manera sintópica y simpátrica con la especie tipo del genero, G. carapo. La nueva especie se diagnostica por una combinación única de rasgos morfométricos, merísticos y osteológicos, así como un patrón característico de bandas pares obscuras no ramificadas e incompletamente separadas, alternando con bandas claras que raramente alcanzan el centro de la línea dorsal en la mitad anterior del cuerpo adquiriendo forma de media luna en la parte abdominal. Gymnotus chaviro es un miembro del grupo de especies de G.carapo, con quien comparte la presencia de dos poros en la porción dorso lateral del preopérculo, bandas con pigmentos obscuros con márgenes ondulados que se parten y/o pierden el contraste con el color de fondo a medida que crece, aleta anal obscura con un claro parche de un pigmento obscuro en borde caudal y más de cuatro dientes en forma de punta de flecha (anteroposteriormente comprimidos) en la porción anterior del dentario. Gym...
We report results of an ichthyological survey of the Lower Urubamba river, a tributary of the Ucayali river located in the southwestern portion of the Amazon Basin in southeastern Peru. Collections were made at low water (July, 2009) from 280 - 310 m elevation, near the town of Sepahua within the Fitzcarrald Arch, an upland associated with Pliocene (c. 4 Ma) uplift of the Peruvian Andes. This is the second of four planned expeditions to the region with the goal of comparing ichthyofaunas across the headwaters of the largest tributary basins in the western Amazon (Juruá, Ucayali, Purús and Madre de Dios). Twenty-one sites were sampled using seine nets, hook lines, cast nets and dip nets. A total of 98 species in 22 families and eight orders were captured and identified. The most diverse families are Characidae (40 spp.) and Loricariidae (20 spp.), and 12 families are represented by a single species. These data suggest that the fish fauna of the Lower Urubamba river near Sepahua is distinct from, and less diverse than, adjacent areas of lowland Amazonia.
Gymnotus tiquie, new species, is described from the Rio Tiquié , a tributary of the Uaupé s (Vaupé s) in the upper Negro basin, Amazonas, Brazil. The new species was collected in non-floodplain (terra firme) streams, where it occurs sympatrically and syntopically with two geographically widespread congeners, the type species of the genus, G. carapo, and G. coropinae. The new species is diagnosed by a unique combination of morphometric, meristic, and osteological traits, and by a characteristic color pattern in which the dark oblique pigment bands, diverse in shape and design, are divided into band-pairs along the length of the body, in which the band-pairs are often recurved (dorsally concave), more variable, and often reticulated in the abdominal region, and in which the pale inter-bands meet at the dorsal midline along most of the length of the body. Gymnotus tiquie is a member of the G. pantherinus species group, with which it shares the presence of one (vs. two) pore in the dorsolateral portion of the preopercle (except in G. pantanal and G. anguillaris), needle-shaped (vs. conical or arrowhead-shaped) teeth on the dentary and premaxilla, and a slender body (BD 5.6-10.6% HL vs. deep 8.7-13.5%, except G. chaviro, G. curupira, G. varzea, G. chimarrao, G. maculosus, G. henni, and G. inaequilabiatus that also have a slender body). Gymnotus tiquie is most similar in overall appearance to G. cataniapo of the upper Orinoco. These two species share three unique features within the G. pantherinus group: dark band-pairs with wavy irregular margins along the length of the body, a long body cavity with 45 or more pre-caudal vertebrae, and a darkly pigmented membrane in the caudal region of the anal fin.Gymnotus tiquie, nova espécie, é descrita para o rio Tiquié, um afluente do rio Uaupés (Vaupés), bacia do alto rio Negro, Amazonas, Brasil. A nova espécie foi coletada em igarapé s de terra firme, onde ela ocorre simpatricamente e sintopicamente com dois congêneres geograficamente amplamente distribuídos, a espécie-tipo do gênero, G. carapo, e G. coropinae. A nova espécie é diagnosticada por uma combinação ú nica de caracteres morfométricos, meristicos e osteoló gicos, e por um padrão de colorido característico no qual as faixas oblíquas escuras, variadas em forma, são divididas em pares de bandas ao longo do corpo, nos quais os pares de bandas são frequentemente recurvados (côncavos dorsalmente), mais variá veis, e frequentemente reticulados na região abdominal, e nos quais as faixas intermediárias pá lidas encontram-se na região dorsal média ao longo da maior parte do comprimento do corpo. Gymnotus tiquie é um membro do grupo de espécies G. pantherinus, com o qual compartilha a presença de um (vs. dois) poros na porção dorsolateral do pré-opérculo, dentes do dentário e pré-maxila em forma de agulha (vs. dentes do dentário e pré-maxila cônicos ou em forma de ponta de flecha) e um corpo alongado (altura do corpo 5.6-10.
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